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Study Says Air Cars Are Inefficient

By Jim Motavalli November 20, 2009 12:00 pmNovember 20, 2009 12:00 pm

There’s no question that people love the idea of compressed-air cars, which have long been under development by the French company Motor Development International and, according to a company spokesman, could be on American roads (after many delays) by 2012.

“It sounds ideal, like we could be free from the constraints of petroleum dependence,” said Andrew Papson, a transportation engineer and associate at the consulting firm ICF International.

But as much as the idea is attractive, Mr. Papson is skeptical about air cars. He finished graduate studies at the University of California, Berkeley, last year and was part of a team at the school that published a paper this week that was critical of air-car claims.

The “Economic and Environmental Evaluation of Compressed-Air Cars,” published in Environmental Research Letters, examined the life cycle of the compressed-air car and concluded that the air car “fared worse than the battery-electric vehicle in primary energy required, greenhouse gas emissions and life-cycle costs, even under very optimistic assumptions about performance. Compressed-air-energy storage is a relatively inefficient technology at the scale of individual cars and would add additional greenhouse gas emissions with the current electricity mix.”

Mr. Papson, who has co-authored a second academic paper that will be presented at the 2010 Transportation Research Board annual meeting, said that compressed air holds less than 1 percent of the energy of gasoline. In an e-mail message, he said that his calculations (based on specifications he said he obtained from M.D.I.) show that the air car would likely have a range of 29 miles. According to the research board report, air cars are “ultimately not viable, comparing poorly to gasoline and electric vehicles in all environmental and economic metrics.”

“Compressed-air cars sound very nice, and they share with electric cars the advantage of not producing any local air pollution on the road, as well as being able to charge from the grid, but electric cars are much more efficient,” said Felix Creutzig, a co-author and post-doctoral fellow, in an e-mail message. “Electric cars are about three times more efficient than compressed-air cars.”

The Environmental Research Letters report does conclude that a hybrid car combining compressed air with a gas engine “is technologically feasible, inexpensive and could eventually compete with hybrid electric vehicles.”

Zero Pollution Motors of New Paltz, N.Y., is licensed to produce compressed-air cars in the United States, said the company’s chief executive, Shiva Vencat, and could do so by 2012. According to Mr. Vencat, the company will start production in Nice, France, in the first quarter of 2010. He said air cars (there are several models that have been shown) have a range of 120 miles at what he called “urban speed.” A proposed range extender, which heats the air with a variety of fuels, including propane or vegetable oil, will be on the second generation of cars.

Asked about academic challenges to the compressed-air car, Mr. Vencat said, “Buy a ticket, go to Nice and try one.”

We are at the stage of winnowing pie-in-the-sky claims from real workable vehicles and products. We are in a efficency green bubble and there are a lot of carpetbaggers and pitchmen elbowing in for the large car market.

Show me the money. Show me the car. Marketing is fluff. The Aptera is a casualty, but a necessary one. There are a lot of evolutionary dead ends as the fossil record shows. Only one lead to Homo sapien.

I do not think it is a coincidence that the only TWO vehicles to meet the NEW 2015 EPA standards look almost identical, same layout and same powertrain design of gas-Hybrid: THE TOYOTA PRIUS and THE NEW HONDA INSIGHT. Is this the future shape of all cars?….at this time the answer is yes.
ALL other auto makers and future designers should take heed. Start mimicking. Copy. Improve . Evolve.
Lots of crazy ideas are in the end laughable .ie. giant flywheel car. Air compression vehicle. Mass transit skateboard. Giant Insect leg walker. Hover car. :)

The Kammback is a more efficient and aerodynamic shape than other more standard teardrop shapes. The Prius and Insight have lower coefficient of drag than the Porsche Boxster. And they are more practical for hauling luggage or groceries.

I have been watching / hoping for a validation of CAV via the automotive x-prize, and was delighted when CAVs were on the initial list. They did not make the design phase cut, and given the 15 years of any-day-now claims from MDI, it could be some serious issues remain.

Solar – Air cycle – cleanest possible?
If the recharge electricity was local solar (e.g. “filling station roof panels and high volume compressed air storage) then, what is the trade off between cost to build, use, and recycle batteries + motors vs cost to build, use, and recycle an air tank + air engine?

Could we save on rare-earth metals, industrial battery construction waste, and recycling’s toxic waste handling by skipping the battery part?

Once again, WEIGHT is a bigger factor. A car that weighs less will be more efficient, as it will have less mass to move along. The Nash Metro achieved better efficiency than its larger contemporaries because it was small and weighed less, but it used the same materials, and followed similar design styles of other vehicles from its time. Aerodynamics add to the overall efficiency, but the Prius and Insight are examples of laziness when it comes to design, as are all of the teardrop shapes and speedforms that are out on the roads today – just put a lump in a wind tunnel, and this is what you get. If you take one of Mazda’s concept designs, make it out of lightweight, yet strong, composite materials, and you’ll get a vehicle that I would bet would exceed the fuel efficiency of the Insight and Prius – I suspect that a “parade float” of the 50’s or 60’s would also get great fuel efficiency if made with composites, and given modern-day mechanicals ( though not matching the Prius or Insight ).

Unfortunately, the cost of composite materials makes this prohibitive on any kind of large scale. How sad this is.

Hi, to all who are really interested in learning more about compressed air cars, have a look at my site http://www.aircars.tk, with allways the latest news. Then decide for yourself whether air cars are a valid alternative.
Thank you

@Tom Evans,
Because of the inherent thermodynamic inefficiencies of compressing air (which produces heat) and rapid expansion (which loses heat to cooling), you’d need a lot more solar panels to fill up your air car than to recharge your battery electric vehicle to travel the same distance. You can improve efficiency by using the heat to warm your house and the cold as air conditioning, but not that much.

All the fake concern about toxic materials from batteries is just fear-mongering. Nickel metal hydride and lithium-ion batteries are no more toxic than other metals that go into a car (unlike the lead-acid battery in every conventional car), and they do get recycled. Even if you put 500 pounds of batteries in a car, the reduction in pollution over 150,000 miles of vehicle operation far outweighs the pollution from their manufacture.

Skierpage, thank you for an extremely relevant observation about the thermodynamic inefficiencies of storing energy in compressed air.

I designed a compressed air powered skateboard for my Senior Design class at the Cal State University at Northridge School of Engineering in 1983.

Among other things, I learned that: 1) the amount of energy stored in the form of compressed air is very low on a per pound basis compared with electric batteries or (especially) gasoline; 2) the requisite high pressure tank is very heavy, and would be an explosion hazard in the event of a collision; and 3) the high-pressure compressor required for home charging would be very expensive, equal to a significant portion of the vehicle cost.

What car is more efficient than the Prius and Insight that is for sale? A Ford Fiesta Econetic Turbo Diesel! Just because it is not for sale in the united states does not mean hybrids are the beez knees.

If you can’t buy it and drive it from home to work, it is not a REALISTIC CAR. We can have imaginary cars in our dreams….but real ones start in the morning and need the windows scraped. Just because something is on sale in Dublin, doesn’t make my commute any easier here in Cincinnati. Be a realist, not a hand waver.

Thanks for bringing science into the compressed-air car story Jim. I strive to do much the same for the MDI story in this month’s issue of IEEE Spectrum magazine. See “Deflating the Air Car” for a readable run of the thermodynamics of MDI’s AirPod minicar.

Although thermodynamics is real, and this particular concept is fantasy, or at least exaggeration, there are some possibilities for using compressed air in situations where there is excess mechanical energy, as mentioned in Fairley’s article. But so are a flywheel, a battery-generator combination, a ‘supercapacitor’, a big spring, or even the prime mover of our youth, the twisted rubber band.
What’s left out of the discussion, however, is whether or not there’s a physical/chemical means of bringing gas to near liquid density at somewhat lower applied pressure that might work with air. Significant work has been done with respect to hydrogen storage for mobile applications out of similar motivation, so I would not rule out a device that would be usable for other gases, like air or a closed-cycle material.
–

What if someone could produce an engine, equal in efficiency to engines now, with compressd air as a by-product of their cycle. What if this engine could produce more stored air than it could expend, therefore never needing to stop and recharge. What if the stored compressed air helps propel the vehicle for free, like having someone help push you up a hill.

Wait a second, someone is doing that now. Its called the scuderi split cycle engine.

The Peter Fairley article (see link in comment #14, above) is more accurate than any of the three journal articles.

The journal articles, although coming to the conclusion that air cars aren’t a great idea, make many basic errors such as assuming a 93% efficient 310 bar compressor. The actual real life efficiency is more like 55%, which makes air cars even more unattractive.

The journal articles also show a lack of understanding of the MDI technology when they treat the MDI air engine as a 2 stage expansion. It is not, and is therefore even more inefficient than the journal articles assume.

The IEEE Peter Fairley article properly describes the MDI system where 49% of the tank energy is lost to a 20 bar regulator even before the air is supplied to the engine.

My name is Armando Regusci we are develoíng vehicles that run with compressed air.
Our engine use a free piston and freewheel.
And we have compressors with the same tecnology
Our efficiency is the best of all the engines and compressors that work with compressed air.
Our engine have for far much more efficiency that Guy Negre car our engine don’t use crankshaft like Guy Negre car.
Compressed air car have much more efficiency that hidrogen car , compressed air is not dangerous like hidrogen.
Compressed air vehicles in comparation with the batetries car, the bateries car need several hours for charge the batteries the compressed air car can by charge in one minute.
After 400 charges the bateries need to be change the carbon fiber tanks can be charges and discharge 100000 time. the bateries is good for one year the carbon fiber tanks have a life time working of 20 years.
you can storage the air without don’t loose energy for 20 years .
The bateries have Cadmium that is very dangerous for the health and the tanks of carbon fiber are polution free.
Compressed air is the best way to storage energy and our vehicles is the best of the of the compressed air vehicles.
I went 2 time to USA I was working in North Texas University I show the a bike running and no body want help and don’t let me go to the news paper.
I am shure that the compressed air tecnology is the energy of the future not only for the vehicles for electricity for heater for air conditioning ,refrigerations and all kind of energy.
Is time to let the people know that this sistem is the best.
Armando Regusci president of the Regusci Air Club Company SA

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